Neutral Triple Gauge Couplings Research Articles

Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4ℓ events with the ATLAS detector at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 ± 0.60 fb, consistent with the next-to-leading-order Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.

Optimal estimation of dimension-8 neutral triple gauge couplings at the e+e− colliders

We investigate the measurement of non-standard ZZV (V = γ, Z) couplings through Z-boson pair production at the e+e− colliders. We adopt the Standard Model Effective Field Theory (SMEFT) approach to study these anomalous neutral triple gauge couplings. There are one CP-conserving and three CP-violating dim-8 SMEFT operators that contribute to ZZV couplings. Using the optimal observable technique, the sensitivity of these new physics couplings has been estimated and compared with the latest experimental limits on dim-8 couplings at the LHC at CERN. The effect of beam polarization and correlations among CP-violating ZZV couplings are discussed. The comparison of statistical limits of new physics couplings between optimal observable technique and contemporary cut-based analysis has also been studied in detail.

Probing anomalous ZZγ and Zγγ couplings at the e+e− colliders using optimal observable technique

We study the anomalous ZZγ and Zγγ couplings that can be probed via Zγ production at the e+e− colliders. We take Standard Model Effective Field Theory (SMEFT) approach to examine these anomalous neutral triple gauge couplings in a model independent way. There are four independent dimension-8 operators that generate these gauge interactions, one of them is CP-conserving and rest three are CP-violating. We adopt optimal observable technique to extract the sensitivity at which these anomalous couplings can be probed at future e+e− colliders and then compare the results with the latest experimental limit obtained at the LHC. We also study the impact and advantage of beam polarization in these precision measurements. Statistical limit (95% C.L.) on individual anomalous couplings as well as the correlation between various couplings have been discussed in detail.

Probe of the anomalous neutral triple gauge couplings in photon-induced collision at future muon colliders

The anomalous ZZγ and Zγγ neutral triple gauge couplings occurred by dimension-eight operators are investigated through the process μ+μ−→μ+γ⁎μ−→μ+Z(νν¯)μ− at the muon collider with s=3, 6, 10 and 14 TeV. The charged lepton pseudo-rapidity, the charged lepton transverse momentum and the transverse missing energy distributions are taken in consideration for the final state of the process in the analysis. The sensitivities of the anomalous couplings are obtained at 95% Confidence Level with integrated luminosity of Lint=1, 4, 10 and 20 ab−1, respectively, according to center-of-mass energies of muon collider taking into account the effects of systematic uncertainties 0%, 3% and 5%. The best limits of anomalous CBB/Λ4, CBW/Λ4, CB˜W/Λ4 and CWW/Λ4 couplings without systematic uncertainty at center-of-mass energy of 14 TeV and integrated luminosity of 20 ab−1 are found to be [-0.01026; 0.00636] TeV−4, [-0.02482; 0.03053] TeV−4, [-0.01830; 0.02510] TeV−4, [-0.06981; 0.07387] TeV−4, respectively.

Prediction for the Anomalous ZZZ and ZZγ Couplings via two Z-boson Production at the CLIC

The non-Abelian nature of the Standard Model (SM) entails the existence of the gauge bosons' self-interactions. The gauge bosons' self-interactions are important to test the SM and see the new physics effects. These effects can be analyzed in the effective theory approach which is the main aim of this study. We examine the ZZZ and ZZγ anomalous neutral triple gauge couplings (aNTGC) via the process e^- e^+→ZZ with both unpolarized and polarized electron beam with the √s=3 TeV at CLIC. In the final state, semi-leptonic decay of Z-bosons (Z→jj , Z→ν_l (ν_l ) ̅ ) are considered. We focused on CP-violating C_BB/Λ^4 , C_BW/Λ^4 , C_WW/Λ^4 and CP-conserving C_(B ̅W)/Λ^4 couplings. The sensitivities are obtained at 95% Confidence Level with luminosities of L_int=5 ab-1, L_int=1 ab-1 and L_int=4 ab-1 for unpolarized, 80% and -80% polarized electron beams, respectively. Obtained sensitivities on anomalous couplings are 3-20 times stringent than the current experimental limits and comparable with the related phenomenological studies in the literature.

Probing neutral triple gauge couplings at the LHC and future hadron colliders

We study probes of neutral triple gauge couplings (nTGCs) at the LHC and the proposed 100TeV $pp$ colliders, and compare their sensitivity reaches with those of the proposed $e^+ e^-$ colliders. The nTGCs provide a unique window to the new physics beyond the Standard Model (SM) because they can arise from SM effective field theory (SMEFT) operators that respect the full electroweak gauge group $SU(2)_L\otimes U(1)_Y$ of the SM only at the level of dimension-8 or higher. We derive the neutral triple gauge vertices (nTGVs) generated by these dimension-8 operators in the broken phase and map them onto a newly generalized form factor formulation, which takes into account only the residual U(1)$_{\rm{em}}$ gauge symmetry. Using this mapping, we derive new relations between the form factors that guarantee a truly consistent form factor formulation of the nTGVs and remove large unphysical energy-dependent terms. We then analyze the sensitivity reaches of the LHC and future 100TeV hadron colliders for probing the nTGCs via both the dimension-8 nTGC operators and the corresponding nTGC form factors in the reactions $ pp(q\bar{q})\to Z\gamma$ with $Z\to\ell^+\ell^-,\nu\bar{\nu}$. We compare their sensitivities with the existing LHC measurements of nTGCs and with those of the high-energy $e^+e^-$ colliders. In general, we find that the prospective LHC sensitivities are comparable to those of an $e^+ e^-$ collider with center-of-mass energy $\leq 1$TeV, whereas an $e^+ e^-$ collider with center-of-mass energy $(3 - 5)$TeV would have greater sensitivities, and a 100TeV $pp$ collider could provide the most sensitive probes of the nTGCs.

Search for the anomalous ZZγ and Zγγ couplings via ννγ production at the CLIC

The non-Abelian gauge structure of the Standard Model implies the presence of the multi-boson self-interactions. Precise measurements in experimental and theoretical studies of these interactions allow not only testing the nature of the Standard Model but also new physics contribution coming from the beyond Standard Model. These interactions can be examined using a model-independent way in effective theory approach that composes the motivation part of this study. In this paper, we examine the anomalous ZZγ and Zγγ neutral triple gauge couplings via the process e−e+→Zγ for the neutrino-antineutrino pair decay of Z boson. It has performed with both unpolarized and polarized electron beams at the Compact Linear Collider with s=3 TeV. The study focused on CP-conserving CB˜W/Λ4 and CP-violating CBB/Λ4, CBW/Λ4, CWW/Λ4 couplings. Obtained sensitivities on the anomalous neutral triple gauge couplings with 95% Confidence Level are given with systematic uncertainties of 0%, 5% and 10% for unpolarized, −80% and 80% polarized electron beams with integrated luminosities of Lint=5ab−1, Lint=4ab−1 and Lint=1ab−1, respectively. Comparing the latest experimental limits and related phenomenological studies, our results on the anomalous neutral gauge couplings are set more stringent sensitivity between 10-30 times of magnitude.

Using a nested anomaly detection machine learning algorithm to study the neutral triple gauge couplings at an e+e− collider

Anomaly detection algorithms have been proved to be useful in the search of new physics beyond the Standard Model. However, a prerequisite for using an anomaly detection algorithm is that the signal to be sought is indeed anomalous. This does not always hold true, for example when interference between new physics and the Standard Model becomes important. In this case, the search of new physics is no longer an anomaly detection. To overcome this difficulty, we propose a nested anomaly detection algorithm, which appears to be useful in the study of neutral triple gauge couplings at the CEPC, the ILC and the FCC-ee. Our approach inherits the advantages of the anomaly detection algorithm been nested, while at the same time, it is no longer an anomaly detection algorithm. As a complement to anomaly detection algorithms, it can achieve better results on problems that are no longer anomaly detection.

The study of neutral triple gauge couplings in the process e+e− → Zγ including unitarity bounds

The neutral triple gauge couplings (nTGCs) provide a unique opportunity to probe new physics beyond the Standard Model. The nTGCs can be described by an effective field theory (EFT), which is valid only under a certain energy scale. One of the signatures that an EFT is no longer valid is the violation of unitarity. We study the partial wave unitarity bounds on the coefficients of nTGCs in the process e+e−→Zγ. In the experiments, the constraints obtained should be tighter than the unitarity bounds, otherwise the results are meaningless, therefore there exists a minimal luminosity for a e+e− collider such as the CEPC to study the nTGCs. To derive the minimal luminosity, the kinematic features and event selection strategy are studied by Monte-Carlo simulation. Both the processes e+e−→ℓ+ℓ−γ and e+e−→jjγ are studied, event selection strategies are discussed. Based on the statistical significance, the expected constraints in experiments are estimated. The required luminosities for the experiments to reach the unitarity bounds are presented.

Search for the limits on anomalous neutral triple gauge couplings via ZZ production in the ℓℓνν channel at FCC-hh

This paper presents the projections on the anomalous neutral triple gauge couplings (aNTGC) via pp→ZZ production in the 2ℓ2ν final state at a 100 TeV proton-proton collider, FCC-hh. The realistic FCC-hh detector environments and its effects taken into account in the analysis. The study is carried out in the mode where one Z boson decays into a pair of same-flavor, opposite-sign leptons (electrons or muons) and the other one decays to the two neutrinos. The new bounds on the charge-parity (CP)-conserving couplings CB˜W/Λ4 and CP-violating couplings CWW/Λ4, CBW/Λ4 and CBB/Λ4 achieved at 95% Confidence Level (C.L.) using the transverse momentum of the dilepton system (pTℓℓ) are [−0.042,+0.042], [−0.049,+0.049], [−0.048,+0.048], and [−0.047,+0.047] in units of TeV−4, respectively.

Constraining CP violating operators in charged and neutral triple gauge couplings

We constrain CP-violating charged and neutral anomalous triple gauge couplings using LHC measurements and projections of diboson and VBF Vjj production, both with subsequent leptonic decays. For triple gauge couplings involving W bosons we analyse differential asymmetries and interpret our results in the SMEFT at dimension-six. For neutral triple gauge couplings, which are dominantly constrained by high transverse-momentum bins, we present the resulting bounds in terms of a general anomalous couplings framework.

Probing new physics in dimension-8 neutral gauge couplings at e+e− colliders

Neutral triple gauge couplings (nTGCs) are absent in the standard model effective theory up to dimension-6 operators, but could arise from dimension-8 effective operators. In this work, we study the pure gauge operators of dimension-8 that contribute to nTGCs and are independent of the dimension-8 operator involving the Higgs doublet. We show that the pure gauge operators generate both $Z\gamma Z^*$ and $Z\gamma\gamma^*$ vertices with rapid energy dependence $\propto E^5$, which can be probed sensitively via the reaction $e^+e^- \to Z\gamma$. We demonstrate that measuring the nTGCs via the reaction $e^+e^- \to Z\gamma$ followed by $Z \to q\bar{q}$ decays can probe the new physics scales of dimension-8 pure gauge operators up to the range $(1-5)$TeV at the CEPC, FCC-ee and ILC colliders with $\sqrt{s}=(0.25-1)$TeV, and up to the range $(10-16)$TeV at CLIC with $\sqrt{s}=(3-5)$TeV, assuming in each case an integrated luminosity of 5/ab. We compare these sensitivities with the corresponding probes of the dimension-8 nTGC operators involving Higgs doublets and the dimension-8 fermionic contact operators that contribute to the $e^+e^-Z\gamma$ vertex.

Sensitivity on anomalous neutral triple gauge couplings via ZZ production at FCC-hh

We study the sensitivity of anomalous neutral triple gauge couplings (aNTGC) via pp rightarrow ZZ production in the 4ell channel at 100 TeV center of mass energy of future circular hadron collider, FCC-hh. The analysis including the realistic detector effects is performed in the mode where both Z bosons decay into same-flavor, oppositely charged lepton pairs. The sensitivities to the charge–parity (CP)-conserving couplings C_{{tilde{B}}W} / Lambda ^{4} and CP-violating couplings C_{WW} / Lambda ^{4}, C_{BW} / Lambda ^{4} and C_{BB} / Lambda ^{4} obtained at 95% Confidence Level using the invariant mass distribution of the 4ell system reconstructing the leading and sub-leading Z boson candidates are [-,0.09, ,, +,0.09], [-,0.21, ,, +,0.21], [-,0.26, ,, +,0.26], and [-,0.10, ,, +,0.10] in units of hbox {TeV}^{-4}, respectively.

The projections on ZZγ and Zγγ couplings via [formula omitted] production in HL-LHC and HE-LHC

We investigate the sensitivity of the anomalous dimension-8 neutral triple gauge couplings via process pp→ννγ with fast detector simulation including pile-up effects for the post LHC experiments. The transverse momentum of the final state photon and missing energy transverse distributions are considered in the analysis. We obtain the sensitivity to the CB˜W/Λ4, CBB/Λ4, CWW/Λ4 and CBW/Λ4 couplings at HL-LHC and HE-LHC with an integrated luminosity of 3 ab−1 and 15 ab−1, respectively. Finally, our numerical results show that one can reach the constraints at 95% confidence level without systematic error on CB˜W/Λ4, CBB/Λ4, CWW/Λ4 and CBW/Λ4 couplings for HL-LHC (HE-LHC) as [−0.38;0.38]([−0.12;0.12]), [−0.21;0.21]([−0.085;0.085]), [−1.08;1.08]([−0.38;0.38]) and [−0.48;0.48]([−0.25;0.25]), respectively. They are better than the experimental limits obtained by LHC.

ZZ→ℓ+ℓ−ℓ′+ℓ′− cross-section measurements and search for anomalous triple gauge couplings in 13 TeV pp collisions with the ATLAS detector

Measurements of $ZZ$ production in the $\ell^{+}\ell^{-}\ell^{\prime +}\ell^{\prime -}$ channel in proton-proton collisions at 13 TeV center-of-mass energy at the Large Hadron Collider are presented. The data correspond to 36.1 $\mathrm{fb}^{-1}$ of collisions collected by the ATLAS experiment in 2015 and 2016. Here $\ell$ and $\ell'$ stand for electrons or muons. Integrated and differential $ZZ \to \ell^{+}\ell^{-}\ell^{\prime +}\ell^{\prime -}$ cross sections with $Z \to \ell^+\ell^-$ candidate masses in the range of 66 GeV to 116 GeV are measured in a fiducial phase space corresponding to the detector acceptance and corrected for detector effects. The differential cross sections are presented in bins of twenty observables, including several that describe the jet activity. The integrated cross section is also extrapolated to a total phase space and to all Standard-Model decays of $Z$ bosons with mass between 66 GeV and 116 GeV, resulting in a value of $17.3 \pm 0.9$ [$\pm 0.6$ (stat.) $\pm 0.5$ (syst.) $\pm 0.6$ (lumi.)] pb. The measurements are found to be in good agreement with the Standard-Model predictions. A search for neutral triple gauge couplings is performed using the transverse momentum distribution of the leading $Z$-boson candidate. No evidence for such couplings is found and exclusion limits are set on their parameters.

Neutral triple and quartic gauge couplings at LEP

The possible existence of neutral triple ZZZ, ZZγ and Zγγ and quartic ZZγγ gauge boson couplings is investigated. Based on data collected at LEP2 at centre-of-mass energies up to 208 GeV no evidence has been found for such couplings. Preliminary limits for neutral triple gauge couplings as obtained from the combination of the LEP experiments are presented.

Neutral triple and quartic gauge couplings at LEP

The possible existence of neutral triple ZZZ, ZZγ and Zγγ and quartic ZZγγ gauge boson couplings is investigated. Based on data collected at LEP2 at centre-of-mass energies up to 208 GeV no evidence has been found for such couplings. Preliminary limits for neutral triple gauge couplings as obtained from the combination of the LEP experiments are presented.

Experimental effects of the off-shell structure in anomalous neutral triple gauge vertices

We discuss differences between on-shell and off-shell treatments in the search for anomalous neutral triple gauge couplings in $\mathrm{e^+ e^-}$ collisions. We find that the usual on-shell framework represents an optimal starting point, covering all scenarios in which a reasonable experimental sensitivity is expected. We show that off-shell effects lead to negligible deviations at the experimental level, provided that $\mathrm{e^+ e^-}\to\mathrm{f}\bar{\mathrm{f}}\gamma$ and $\mathrm{e^+ e^-}\to\mathr performed in regions where $\mathrm{Z}^*\to\mathrm{f}\bar{\mathrm{f}},\mathrm{f^\prime}\math production is dominant. For consistency reasons, we advocate the use of a natural extension of the on-shell definitions, which takes into account the correct off-shell dependences. Contrary to what has been recently suggested in the literature, we find that no $SU(2)_L\times U(1)_Y$ constraints among neutral triple gauge couplings can be imposed in a general case.